How the Heart Works?(DOCTOR STEEMIT:@MEHDIKH19)

The heart is responsible for circulating blood throughout the body. It is about the size of your clenched fist and sits in the chest cavity between your two lungs. Its walls are made up of muscle that can squeeze or pump blood out every time the heart "beats" or contracts.

Blood is essential. In addition to carrying fresh oxygen from the lungs and nutrients to your body's tissues, it also takes the body's waste products, including carbon dioxide, away from the tissues. This is necessary to sustain life and promote the health of all the body's tissues.

The structure of your heart:
Diagram showing the four chambers of your heart
Your heart is made up of three tissue layers:
Pericardium – a thin outer lining that protects your heart
Myocardium – the thick muscular tissue that contracts and squeezes blood out of your heart
Endocardium – a thin inner lining that also provides protection.

The four heart valves are:

1.the tricuspid valve, located between the right atrium and the right ventricle;
2.the pulmonary (pulmonic) valve, between the right ventricle and the pulmonary artery;
3.the mitral valve, between the left atrium and left ventricle; and
4.the aortic valve, between the left ventricle and the aorta.

Coronary arteries
Coronary arteries supply the heart muscle with blood. The left and right coronary arteries divide many times to spread over the heart muscle wall and give it blood and oxygen.

The heart's control system:

A heartbeat is caused by an electrical impulse traveling through the heart. The heart's built-in electrical system controls the speed of its pumping. The electrical impulse originates in the sinus node which functions as the heart's natural pacemaker. The sinus node is most often located in the top of the right atrium.

Cardiac output: The amount of blood the heart pumps through the circulatory system in a minute. The amount of blood put out by the left ventricle of the heart in one contraction is called the stroke volume. The stroke volume and the heart rate determine the cardiac output. A normal adult has a cardiac output of 4.7 liters (5 quarts) of blood per minute.

Tachycardia:
refers to a fast resting heart rate - usually at least 100 beats per minute. Tachycardia can be dangerous, depending on its underlying cause and on how hard the heart has to work.

bradycardia:
A heart rate of less than 60 beats per minute (BPM) in adults is called bradycardia. What's too slow for you may depend on your age and physical condition.

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